How is progress measured on board the US aircraft carrier which is playing a key role in the fight against Islamic State?

The aircraft carrier USS Carl Vinson, plying the waters of the Gulf, represents a big slice of the coalition effort being used to pound the self-proclaimed Islamic State in Syria and Iraq - an onslaught that has been going on for the best part of five months now.

It is a floating town of more than 5,000 souls and 60 fighter aircraft engaged in a costly and complex campaign.

Each time it launches one of its jets, catapulting it over the green waters south of Iran, the event is so dramatic and inherently dangerous that it would be understandable if many a spectator forgot the question - is this air offensive working?

It's extremely hard for Western reporters to seek the answers to that on the ground, in Mosul or Raqqa. But we can be on board the carrier, speaking to those carrying out this operation, as I was for four days, gauging their sense of the task, its challenges, and whether it's achieving results.

This week the United States will use meetings on the margins of the UN General Assembly to finalise its coalition for fighting Islamic State (IS) in Iraq and Syria.

The White House has spoken of rallying 40 countries to the cause, but since this planned group cuts across the Sunni/Shia divide, as well as harnessing long-standing Middle East rivals, many have asked whether it's really possible.

About Mark

Mark has covered diplomatic and defence matters for more than 20 years at the BBC.

His major stories have included: the 1990 invasion of Iraq and subsequent Desert Storm campaign; the collapse of the Soviet Union; the Oslo peace process in the Middle East; the wars that broke out in the former Yugoslavia in the mid-1990s as well as the diplomacy that stopped them; the Second Palestinian Intifada; 9/11 and its aftermath; the Coalition campaigns in Afghanistan and Iraq; and the Arab Spring.

Before joining the BBC as a reporter he was Defence correspondent for The Independent newspaper for four years, covering the end of the Cold War and the Soviet withdrawal from Afghanistan.

He is also the author of several books on military matters, both current and historical. Mark read International Relations at the London School of Economics and served for a short time in the British Army.